/Engine/Source/Runtime/Slate/Public/Framework/Notifications/NotificationManager.h
Begin a progress notification. These notifications should be used for background work not blocking work. Use SlowTask for blocking work
NotificationHandle A handle that can be used to update the progress or cancel the notification
[FProgressNotificationHandle](API\Runtime\Slate\Framework\Notifications\FProgressNotificationHandle) StartProgressNotification ( [FText](API\Runtime\Core\Internationalization\FText) DisplayText, int32 TotalWorkToDo )